Textures and Microstructures, 1995, Vol. 23, pp. 257-263 Reprints available directly from the publisher Photocopying permitted by license only (C) 1995 OPA (Overseas Publishers Association) Amsterdam B.V. Published under license by Gordon and Breach Science Publishers SA Printed in Malaysia EFFECT OF CRYSTAL ROTATION ON LIMIT STRAINS OF TEXTURED MATERIALS UNDER EQUI-BIAXIAL TENSION K. C. CHAN Department of Manufacturing Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong Kong (Received 30 March 1995) In this paper, a numerical procedure has been proposed to predict limit strains of textured sheets under equi-biaxial tension by means of the MK model and taking into account of crystal rotation. Limit strains have been predicted for three common crystallographic orientations and an annealed aluminium sheet. The effect of crystal rotation on limit strains was shown to be significant. However, no general trend of the effect has been observed. It is argued that the effect is quite complicated and dependent on various factors such as the initial orientation or texture, groove orientation and the initial inhomogeneous factor. The incorporation of texture change in the analysis of sheet metal forming was found essential. KEY WORDS: Limit strains, texture, crystal rotation and sheet metals. INTRODUCTION Since the introduction of the concept of forming limit diagram by Keeler and Backofen (1963) to represent acceptable limit strain during sheet metal forming, it has become a hot research topic for decades and a considerable amount of experimental and theoretical studies have been carried out. Among the earliest theories of the forming limit diagrams. Marciniak and Kuczynski (MK) (1967) have probably proposed the most influential hypothesis for the limit strains prediction. They postulated the existence of an initial imperfection in the sheet which will develop into a groove running in a direction perpendicular to the larger principal stress. The hypothetical groove served as the nucleus of a neck in their model. After then, much theoretical efforts have been made trying to explain and assign the value of the incipient groove depth. Tadros and Mellor (1975) suggested that the incipient grooves may appear during stable plastic flow but that a single groove will not exhibit continuing growth until diffuse necking occurs. They therefore proposed that the MK theory should be applied to the material at the time when diffuse necking sets in. Yamaguchi and Mellor (1976) and Parmar and et al. (1977) have taken explicit account of the influence of grain anisotropy in biaxial stretching. In these models it is assumed that incipient grooves are formed within the roughened surfaces and that, in stretching beyond diffuse instability, strain localization develops within the deepest groove in accordance with the MK model. In the damage mechanics model of the forming limit, 257
EFFECT OF CRYSTAL ROTATION ON LIMIT STRAINS OF TEXTURED MATERIALS UNDER EQUI-BIAXIAL TENSION
May 19, 2023
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